1. Field of the Invention
The present invention relates to the manufacture of semiconductor wafers, and in particular to a system allowing non-invasive, continuous local and remote sensing of the internal environmental characteristics of transportable containers.
2. Description of Related Art
A Standard Mechanical Interface (“SMIF”) system proposed by the Hewlett-Packard Company is disclosed in U.S. Pat. Nos. 4,532,970 and 4,534,389. The purpose of a SMIF system is to reduce particle fluxes onto semiconductor wafers (“wafers”) during storage and transport of the wafers through the semiconductor fabrication process. This purpose is accomplished, in part, by mechanically ensuring that during storage and transport, the gaseous media (such as air or nitrogen) surrounding the wafers is essentially stationary relative to the wafers, and by ensuring that particles from the ambient atmosphere do not enter the immediate wafer environment. This environment may be referred to herein as a “clean environment.”
A SMIF system has three main components: (1) sealed pods used for storing and transporting wafers and/or wafer cassettes; (2) an input/output (I/O) minienvironment located on a semiconductor processing tool to provide a clean space (upon being filled with clean air) in which exposed wafers and/or wafer cassettes may be transferred to and from the interior of the processing tool; and (3) an interface for transferring the wafers and/or wafer cassettes between the SMIF pods and the SMIF minienvironment without exposure of the wafers or cassettes to contaminants. Further details of one proposed SMIF system are described in the paper entitled “SMIF: A TECHNOLOGY FOR WAFER CASSETTE TRANSFER IN VLSI MANUFACTURING,” by Mihir Parikh and Ulrich Kaempf, Solid State Technology, July 1984, pp. 111–115.
SMIF pods are in general comprised of a pod door which mates with a pod shell to provide a sealed environment in which wafers may be stored and transferred. “Bottom opening” pods 100, as illustrated in FIG. 1A, are pods where the pod door 101 is horizontally provided at the bottom of the pod 100 and mates to pod shell 103. The wafers are supported in a cassette 105 which is in turn supported on the pod door 101. “Front opening” pods 110 as illustrated in FIG. 1B, also referred to as front opening unified pods, or FOUPs, include a pod door 111 that is located in a vertical plane and mates with pod shell 113. The wafers (not shown) are supported either in a cassette (not shown) mounted within the pod shell 113, or to shelves 115 mounted within the pod shell 113.
In order to transfer wafers between a bottom opening or front opening pod and a process tool 505 (FIG. 5) within a wafer fabrication facility, the pod is typically loaded either manually or automatedly onto a load port assembly 507 (FIG. 5) which is typically either mounted to, or part of the process tool 505. The load port assembly 507 includes an access port which, in the absence of a pod, is covered by a port door (not shown). Upon loading of the pod on the load port assembly 507, the pod door aligns against the port door in both bottom opening and front opening systems.
Once the pod is positioned on the load port assembly 507, mechanisms within the port door unlatch the pod door from the pod shell and move the pod door and port door to a position which allows access to the wafers by the processing tool 405. The pod shell remains in proximity to the now exposed access port so as to maintain a clean environment that includes the interior of the process tool and the pod shell.
In bottom opening systems, the port door, with the pod door 101 and wafer-carrying cassette 105 supported thereon, is lowered into the load port assembly 507. A wafer handling robot within the load port assembly 507 or process tool 505 may thereafter access particular wafers from the cassette for transfer between the cassette and the process tool. In front opening systems, the wafer handling robot may access the wafers directly from the pod shell 113 for transfer between the pod 110 and the process tool 505.
Systems of the above type protect against particle contamination of the wafers. Particles can be very damaging in semiconductor processing because of the small geometries employed in fabricating semiconductor devices. Typical advanced semiconductor processes today employ geometries which are one-half μm and under. Unwanted contamination particles which have geometries measuring greater than 0.1 μm substantially interfere with 1 μm geometry semiconductor devices. The trend, of course, is to have smaller and smaller semiconductor device geometries which today in research and development laboratories approach 0.1 μm and below.
As device geometries continue to shrink, contamination particles and molecular contaminants have become an important concern in semiconductor manufacture. There are several sources that cause contamination of semiconductor wafers as they travel through a fabrication process. For example, during a manufacturing process, certain gases, fluids, pressures, coherent and incoherent light, vibrations, electrostatic charge, and contaminants may affect the final yield of semiconductors. Therefore, it is important to control each of these parameters within a pod during the fabrication process.
Sealing the environment within a pod in accordance with SMIF technology discussed above has markedly improved a manufacturer's ability to control the environment surrounding semiconductor wafers. However, pods are frequently opened, both automatedly at load port assemblies for wafer transfer, and manually by technicians, for example during pod cleaning. Moreover, pods often include valves for allowing the transfer of fluids to and from the sealed pod. Each of these operations and pod features can be potential sources of contaminants to semiconductor wafers within a pod.
It is known to perform wafer lot testing, where random or problem pods are selected for internal environmental characteristic testing during or after device formation on the wafers. While such operations are capable of identifying problems after they occur, known testing systems are not intended to pinpoint the time or location at which the problems occur. Thus, such testing operations are often performed too late to prevent contamination to a wafer lot. Moreover, where a contaminated pod is allowed to continue through the fabrication process, it often contaminates other processing tools and wafer lots. Further still, conventional testing operations are not intended to identify the areas within the fabrication facility which are introducing contaminants to the wafers.
Accordingly, there is a desire to provide an apparatus and method for actively monitoring the environment within a pod and processing stations.